1. Technical Field of the Invention
The present invention relates generally to apparatus for producing blocks of dry ice from liquid carbod dioxide. More particularly, it relates to an improved apparatus which will rapidly and continuously produce brick-shaped blocks of dry ice, and which is designed to be especially useful for restaurants, ice cream shops, confectionaries, and the like.
2. Description of the Prior Art
The basic process for making block dry ice from liquid carbon dioxide has long been known, and involves first spraying the liquid carbon dioxide into a chamber to form dry ice snow, and then compressing the snow into a block. Over the years various kinds of apparatus for carrying out this basic process have been devised, and typical of such conventional apparatus is that which is the subject of Great Britain Complete Specification No. 433,018, accepted Aug. 7, 1935. Referring to the drawings of the present application, FIGS. 7 and 8 illustrate the prior art as described in this British patent.
As shown in said FIGS. 7 and 8, a charging cylinder 50 is provided with an inlet nozzle 51 at its upper end, and is positioned vertically above a vertically movable press cylinder 53. A transversely movable shutter 52 is positioned between the cylinders 50 and 53, and is operable by a hydraulic actuator 54. The press cylinder 53 carries an annular piston 58 thereon that is slidable within a cylinder 58a, and which is moved toward and away from the shutter assembly by hydraulic pressure. A press plunger 55 is mounted for vertical movement within the press cylinder 53, and carries a piston 56 on its lower end that is received within a cylinder 56a and which is operable by hydraulic pressure to raise and lower the press plunger 55.
Liquid carbon dioxide is sprayed into the charging cylinder 50 through the inlet nozzle 51, with the shutter 52 in a closed position. As the carbon dioxide is sprayed from the nozzle 51 it changes to dry ice snow through adiabatic expansion. and accumulates in the charging cylinder. When a sufficient quantity of dry ice snow has been formed the shutter 52 is opened by the hydraulic actuator 54, and the snow then falls by gravity into the lower, press cylinder 53, which has been elevated so that its upper end is in contact with the shutter assembly. The shutter 52 is then closed and the press plunger 55 is elevated by hydraulic pressure, to form a block of solid dry ice 57 from the snow. White the press plunger 55 is operating, the charging cylinder 50 is again sprayed with liquid carbon dioxide to form the next charge of dry ice snow for the press cylinder 53.
After the block 57 has been formed the press cylinder 53 is lowered while the press plunger 55 remains elevated, until the respective components reach the relationship shown in FIG. 8, wherein the block 57 of dry ice has been pushed from the cylinder 53 and stands exposed on the press plunger 55. The block 57 is then removed, and the apparatus is ready for another cycle.
While the apparatus of the noted British patent can successfully produce cylindrical blocks of dry ice, it is not fully satisfactory for all applications, especially in those instances where considerable quantities of brick-shaped dry ice need to be produced in minimum time, with a minimum of labor. Among the problems with such prior apparatus are the following:
1. As will be noted from the brief description given of the apparatus of the British patent, the press cylinder 53 must be vertically movable and must be repeatedly driven up and down by hydraulic pressure to provide for removal of the formed dry ice block 57. This requires a rather complicated and expensive mechanical structure which must be maintained, and which is subject to wear and breakdown. PA1 2. In order to provide for automatic operation of the device of the British patent, transferring means must be added thereto to automatically remove the dry ice block 57 after the press cylinder 53 has been lowered. Any such transferring means must be of a rather complicated esign, so as not to interfere with the raising and lowering of the press cylinder 53. PA1 3. Because the dry ice snow supplied into the press cylinder 53 from the charging cylinder 51 in the apparatus of the British patent must have a low density, it is necessary to have a lengthy press cylinder 53 in order to produce large blocks of solid dry ice. This means that the press cylinder 53 and the hydraulic actuator 56 must both have lengthy strokes, which increases the size of the apparatus and hence its cost. PA1 4. During compression of the dry ice snow in the press cylinder 53 of the apparatus described in the British patent, any gaseous carbon dioxide contained in the snow will be shut in the solid dry ice block 57. This trapping of gaseous carbon dioxide is undesirable in that it affects the speed and quality of the pressing operation, and results in dry ice of a quality that is uneven and which is prone to early cracking and breakup. PA1 5. In order to operate the device of the British patent continuously, two shutters must be installed. Further, continuous operation of the device in the British patent will result in some of the dry ice snow adhering to the walls of the charging cylinder 51 and remaining therein, which makes it difficult to constantly produce solid dry ice blocks of uniform size and weight. PA1 1. By utilizing the shutter assembly, in cooperation with the press piston, to automatically remove the just produced block of dry ice from the apparatus, the need to have one or more movable molds of the type shown in the cited British patent is eliminated. Instead, the molds can be fixed to a supporting frame, and the whole apparatus is mechanically less complicated and expensive. PA1 2. By precompressing the dry ice snow in the upper mold, certain advantages are obtained. First, because the charge block entering the lower mold has already been partially compressed, the stroke distance of the press piston and the overall length of the lower, press mold can be considerably shorter than in apparatus like that shown in the British patent. This reduces the overall height of the apparatus and its weight, making the resultant machine less expensive and more adaptable to different work locations. Secondly, utilization of the precompressing piston to move the precompressed charge block of dry ice snow into the lower mold removes effectively all of the dry ice snow from the upper mold, which helps assure the uniform production of the brick-shaped blocks of dry ice. Third, the precompressing action and the dropping of the precompressed charge into the lower mold helps the escape of carbon dioxide gas, thus improving the efficiency of the final compression step and the quality of the resultant dry ice blocks. PA1 3. The use of a breathing, porous material for the shutter and portions of the molds allows the escape of carbon dioxide gas to occur during the two compressing steps, which reduces the required capacity of the hydraulic actuators, improves the overall efficiency of the apparatus, and improves the quality of the produced dry ice blocks.
There is need for an apparatus for making brick-shaped blocks of dry ice from liquid carbon dioxide that minimizes the size of the equipment, requires a minimum of moving elements, controls the problem of trapping gaseous carbon dioxide in the dry ice, and which can repeatedly and rapidly produce dry ice blocks of high quality and substantially uniform characteristics. The apparatus of the present invention is intended to fulfill that need.